You can’t have 24/7 100% aircraft coverage. There is still air defence to contend with as well. From Zhuhai air show there were many shipping container launched missiles. Should the situation deteriorate, I’m sure it would not be hard to develop something similar in Taiwan.
Yes you can have 24/7 air coverage, especially with UCAVs.
Taiwan is cursed by geography in being too close to China and being too small an island that it has zero strategic depth. Everything on the island can be monitored, and anything on the island can be hit within a matter of minutes by missiles launched from the mainland.
It would also be extremely foolish to just take it for granted that anything China can develop Taiwan could too.
And even if Taiwan does develop shipping container AShMs, so what? Without radar support, those missiles would be essentially useless beyond visual range of their targets. Also, unless we are talking about hypersonics, lone AShMs have almost no chance of getting through modern fleet air defences. They need to be fired in large numbers and precisely co-ordinated to arrive on target at the same time to have any chance of getting through.
That is the dilemma, the bigger and more sophisticated the attach, the greater the chance of it being detected before it could be launched.
It’s no coincidence that China is putting radars and EW pods on its UCAVs. Those would be perfect for SEAD/DEAD ops as well as detecting and taking out AShM search and targeting radars.
After the initial first day of conflict battles, I would expect the PLA to permanently park a few dozen UCAVs over Taiwan 24/7 supporting dozens of J16s, who will also act as QRF.
Once the actual invasion starts, expect those numbers to at least double or triple.